Duplex radio signaling set



March 13, 1928. 1,662,126

R. K. POTTER DUPLEX RADIO SIGNALING SET Filed Oct. 5L 1925 Oscillator MH I 21L /4 Receiverfl oparatms 22 Q IN VEN TOR BY WK A TTORNEY PatentedMar. 13, lilZ-fii.

RALPH K. POTTER, 01E NEW YORK, N. K, ASSIGNOR T AMERICAN TELEPHONE ANDTELEGRAPH COMPANY, A CORPORATION 0? NEW YORK.

DUPLEX RADIO SIGNALING SET.

Application filed October 31,1925. Serial lt'o. $630M.

This invention relates to improvements in duplex carrier transmissionsystems.

The invention provides arrangements whereby in a radio or carrier setthe transit mitting or receiving apparatus may be rendered operativealternately in response to currents from the microphone of the set. oaccomplish this purpose a vacuum tube s provided connected to thetransmitter circuit M) which may be rendered inoperative by thealternating current potentials impressed on its grid from thetransmitter circuit. This vacuum tube acts to either block the operationof the oscillator in the transmitter set and render the receivingapparatus operative or vice versa. Other features and objects of theinvention will appear more fully from the detailed description thereofhereinafter given. The invention may be more fully understood from thefollowing description to gether with the accompanying drawing in theFigures 1 and 2 of which are shown a preferred form of the invention anda modi 2a fication thereof.

In the arrangements illustrated in Fig. 1 the sending apparatuscomprises the trans mitter 1 coupled through a transformer 2 to a vacuumtube 3. The signals from the 3o transmitter 1 will be impressed on thetube 3 I,

and will thence be transmitted to the oscillator tube 4 where they willbe superimposed on a carrier frequency and thence transmitted out overan antenna circuit 5 in a a5 manner well known in the art. Bridgedacross the output circuit of the tube 3 is a circuit 6 leading to theinput of a vacuum tube 7, known as the blocking tube. A condenser 8 anda leak resistance are associated to with the grid of the blocking tubeas shown. When the transmitter 1 is actuated by speech waves analternating potential will be applied to circuit 6 and to the grid ofthe blocking tube 7. If this alternating potential is thus impressed onthe grid of tube 7 the electrons will accumulate upon the grid duringeach positive halt cycle and will be detained, there by the blockingcondenser 8, leak resistance 9 determining an the maximum value to whichthe accumulated grid potential will be built u If this impressedalternating potential is of sufficient magnitude it will tend to forcethe grid to a suficient negative potential to as" block the flow ofcurrent from the filament to the plate. In other words, when thetransmitter 1 is actuated by speech the grid of the blocking tube willbe given a sufficiently great negative potential to prevent the normalcurrent from flowing in the plate circuit of the tube 7. The effect ofthis action of blocking the current flow in the plate circuit will havea certain eitect on the operation of the oscillator tube 4 which willnow be explained. The plate circuit of the blocking tube 7 includes aresistance 11 and the battery 10 poled as illustrated. The filampnt ofthe oscillator tube 4 is connected by conductors 23 and 22 to thenegative pole of battery 10. The grid of oscillator tube 4 is connectedto a battery 12 poled as shown. Battery 12 is connected to resistance 11which in turn is connected to the positive pole of battery 10. Hence thepotential of the grid of the oscillator tube 4 with respect to 1tsfilament depends upon the cumulating effect of the following factors:namely, the potential applied thereto from battery 12, the potentialapplied from battery 10, and the effect of the potential drop throughresistance 11. The battery 10, as poled, will tend to give the grid oftube 4 a positive potential with respect to its filament. The

attery 12, as poled, will oppose the potential of battery-10 and bringthe potential of the grid to a point such that it will be sufficientlynegative with-respect to the filament so that the tube will oscillatesatisfactorily. When a current is flowing in the plate circuit of theblocking tube 7, the drop through the resistance 11 will further tend tooppose the effect of battery 10 and will further change the potential ofthe grid of 7 tube 4 so that it will become so ne ative with respect toits filament that the tu e will fail to function and will not oscillate.It will be seen that the normal state of adairs, when the transmitter 1is not in use, will be that current will flow normally in the platecircuit of the blocking tube and cause the drop through the resistance11 to have such an eilect on the potential of the oscillator grid thatthe oscillator will fail to function. However, when the transmitter 1 isactuated, theblocking tube 7, as has been pointed out, reduces or evensto s the current flow in its plate circuit an hence the current flowthrough resistance 11 is reduced or closes. The cessation of currentflow through resistance 11 causes this resistance to have no effect onthe potential of the grid of the'oscillator which will now depend onlyupon the cumulative effect of the applied potentials of batteries 10 and12. It has already been pointed out that under these conditions the gridof the oscillator is of a potential proper for the tubeto oscillate.

= Accordingly, the oscillator tube is normally rendered inoperativebythe blocking tube,

but when the transmitter is actuated by speech the blocking tube isaffected thereby to allow the operation of the oscillator.

The receiving circuit comprises the loop antenna 13 connected to theseries of vacuum tubes 14, 15 and 16 which comprise the detectoramplifier system. The tube 16 has in its output circuit a receiver 17.The condenser 24 and the inductance 20 are provided as shown in thereceiver circuit for the purpose of keeping the transmitter oscillationsoil the receiver grids during the time modulation takes place in thetransmitting portion of the apparatus. The receiver grids have potentialapplied to them from the battery 18. The grid of tube 14 is connectedover conductor 26, loop 13, conductor 25, to the negative pole ofbattery 18. The grids of tubes 15 and 16 are connected over conductor 27to the negative pole of battery 18. Hence a negative potential frombat/- tery 18 is applied to all of the receiver grids. The receiverfilaments are connected over conductors 29 and 28, through resistance19, to the positive pole of battery 18 and hence will have a positivepotential applied thereto. As has been pointed out heretofore, whencurrent is flowing in the plate circuit of the blocking tube 7, the dropthrough the resistance 11 tended to oppose the positive potential effectof battery 10. In like manner, when current is flowing in the platecircuit of the blocking tube 7, the drop through the resistance 19 willtend to oppose in the receiver filament circuits the positive potentialeffect of battery 18. This will reduce the potential difference betweenthe grids and filaments of the receiver to a point where the tubes willoperate satisfactorily. It is ointed out that this is the normal stateof a airs when the receiver 1 is not actuated by speech. Accordingly,whenever the transmitt-er ortion of the apparatus is not operating thereceiver will e in condition for operation. As has been pointed outheretofore when the transmitter is operated, the current flow in theplate circuit is stopped. This has the eifect of cutting out thepotential drop through resistance 19 in the filament circuits of thereceiver tubes. Accordingly, the normal positive potential of thebattery 18, without any reduction due to the dro through resistance 19,will be applied to t e receiver filaments. This will result in anincrease in the potential drop between the grids and filaments. In otherwords, the

grid potentials will be reduced to a point so negative with respect tothe filaments that the receiver tubes will not function. Accordingly, itwill be seen that as soon as speech is impressed on the transmitter, thereceiver apparatus Will be prevented from functioning.

In Fig. 2 is illustrated an alternative form of the invention. A circuitincluding a transmitter 1 is coupled through a transformer 2 to thecircuit 3 of a duplex vacuum tube modulator which comprises vacuum tubes4 and 5' and an output transformer 6. Coupled through a transformer 7 tothe modulator. circuit is a circuit 8 leading to an oscillator whichincludes the vacuum tube 9'. The voice waves impressed on thetransmitter will in turn be impressed on the modulator circuit 3. Theoscillator through transformer 7 will supply a carrier frequency forthese voice waves. The arrangement is a conventional showing of abalanced modulator which results in the elimination of the unmodulatedcarrier. Inductively related to the transmitter circuit is a circuit 10'leading to the grid of a vacuum tube 13. This tube is a blocking tubesimilar to the blocking tube of Fig. 1. The blocking condenser 12' andthe leak resistance 11 are provided as shown in the circuit 10.

As has been previously described in connection with Fig. 1, thealternating current potentials impressed on circuit 10 will operate tostop the normal flow of current in the plate circuit of the blockingtube 13. The plate circuit of tube 13 is as follows: plate of tube 13,battery 14, conductor 15, resistance 16', winding of relay 17 conductors18 and 19 to the filament of tube 13'. When the transmitter l is notbeing actuated by s eech waves, current will normally flow in t is platecircuit and will hold the relay 17 operated. The grid filament circuitof the oscillator tube 9 is as follows: grid of tube 9, battery 24',conductor 25', resistance 16', winding of relay 17', conductors 18 and26 to the filament of tube 9. The battery 24 is so poled that the gridof the tube will have a negative otential with respect to its filament.Furt ermore, the battery 24. is of the proper value so that withouttaking other factors into consideration, the potential drop betweenfilament and grid will be just sufiicient so that the tube will operateproperly and its circuit will function as an oscillator. However, itwill be seen that the resistance 16' is included bothin the platecircuit of the blocking tube and the grid filament circuit of theoscillator tube. When current is flowing in the plate circuit of theblocking tube, the potential drop across the resistance 16 will augmentthe effect of battery 24' and will increase the potential differencebetween grid and filament of the oscillator tube to such an extent thatthe grid will be so negativein potential with respect to the filamentthat the tube will fail to operate. However, when speech is impressed onthe transmitter 1 and the blocking tube ceases to function, there willbe no drop through resistance 16 and the tube 9 and its associatedcircuit will function asan oscillator. Under this condition, namely whenthe current flow in the plate circuit of the blocking tube is cut ofi byspeech, the relay 17 will release. This will open the circuit from theloop antenna 20 to the receiver apparatus 21. The receiver apparatus 21is shown schematically as it may be of any desired type. Connected tothe receiver apparatus is a circuit 22' leading to the receiver 23.

While the arrangements of the invention have been disclosed as embodiedin certain specific forms, it is understood that they may be embodied inmany and other widely varied forms without departing from the spirit ofthe invention as defined in the appended claim.

What is claimed is:

.A carrier signaling set comprising transmitting apparatus including ahigh fre quency oscillator circuit, a low frequenc signaling circuitassociated therewit whereby the high frequency oscillations may bemodulated by the low frequency signals, a vacuum tube circuit having itsgrid circuit connected to said low frequency signaling circuit wherebythe potential of said grid will be determined by the low frequencysignaling currents, means controlled by said grid potential forcontrolling the current flow in the plate circuit of said tube, aresistance included in the plate circuit of said tube, the potentialdrop across said resistance being controlled by the current flow in saidplate circuit, and means controlled by said potential drop across saidresistance for controlling said oscillator circuit.

In testimony whereof, I have signed my name to this specification this27th day of October, 1925.

RALPH K. POTTER.

